AST3020. Lecture 09 Theory of transitional and debris disks
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Transcript of AST3020. Lecture 09 Theory of transitional and debris disks
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AST3020. Lecture 09Theory of transitional and debris disks
The roles of radiation pressureBeta Pictoris as a young solar systemSome observed examples and their non-symmetric morphologyPossible mechanisms of structure formation: artifacts or background objects planets and stars internal disk dynamics: local dust release + avalanche intrinsic disk instabilities (optically thick disks)
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Radiative blow-out of grains (-meteoroids, gamma meteoroids)
Dust avalanches
Radiation pressure on dust grains in disks
Neutral (grey)scattering from s> grains
Repels ISM dust Disks = Nature, not nurture!
Enhanced erosion;shortened dust lifetime
Orbits of stable -meteoroids are elliptical
Dust migrates,forms axisymmetric rings, gaps
(in disks with gas)
Short disk lifetime
Size spectrum of dust has lower cutoff
Weak/no PAH emission
Quasi-spiral structure
Instabilities (in disks)1
Age paradox
Coloreffects
Limit on fIRin gas-free disks
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Structure in transitional and debris disks
- very common - visibly non-axisymmetric
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AB Aur : disk or no disk?
Fukugawa et al. (2004)
another “Pleiades”-type star
no disk
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Hubble Space Telescope/ NICMOS infrared camera
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HD 141569A is a Herbig emission star>2 x solar mass, >10 x solar luminosity,Emission lines of H are double, because they come from a rotating inner gas disk. CO gas has also been found at r = 90 AU. Observations by Hubble Space Telescope (NICMOS near-IR camera).
Age ~ 5 Myr, a transitional disk
Gap-opening PLANET ?So far out?? R_gap ~350AU
dR ~ 0.1 R_gap
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HD 14169A disk gap confirmed by new observations (HST/ACS)
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HD141569+BC in V band HD141569A deprojected
HST/ACS Clampin et al.
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The danger of overinterpretation of structure
Are the PLANETS responsible for EVERYTHING we see? Are they in EVERY system?
Or are they like the Ptolemy’s epicycles, added each time we need to explain a new observation?
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FEATURES in disks: (9)
blobs, clumps ■streaks, feathers ■rings (axisymm) ■rings (off-centered) ■inner/outer edges ■disk gaps ■warps ■spirals, quasi-spirals ■tails, extensions ■
ORIGIN: (10)
■ instrumental artifacts, variable PSF, noise, deconvolution etc.■ background/foreground obj.■ planets (gravity)■ stellar companions, flybys■ dust migration in gas■ dust blowout, avalanches■ episodic release of dust■ ISM (interstellar wind)■ stellar UV, wind, magnetism■ collective eff. (selfgravity)
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FEATURES in disks:
blobs, clumps ■streaks, feathers ■rings (axisymm) ■rings (off-centered) ■inner/outer edges ■disk gaps ■warps ■spirals, quasi-spirals ■tails, extensions ■
ORIGIN:
■ instrumental artifacts, variable PSF, noise, deconvolution etc.
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FEATURES in disks:
blobs, clumps ■streaks, feathers ■rings (axisymm) ■rings (off-centered) ■inner/outer edges ■disk gaps ■warps ■spirals, quasi-spirals ■ tails, extensions ■
ORIGIN:
■ background/foreground objects
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Source: P. Kalas
?
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AU Microscopii and its less inclined cousin
This is a coincidentally(!) aligned background galaxy
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FEATURES in disks:
blobs, clumps ■streaks, feathers ■rings (axisymm) ■rings (off-centered) ■inner/outer edges ■disk gaps ■warps ■spirals, quasi-spirals ■tails, extensions ■
ORIGIN:
■ stellar companions, flybys
Stellar and planetary perturbations =>interesting prospect of finding planets by their imprint on dust
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Kalas and Larwood initially thought they detected ripples on oneside of the Beta Pic disk. Later, evidence for the reality of most ripples disappeared.
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Structure from stellar encounterDoesn’t work in case of beta Pic (despite claim by Kalas and Larwood ca. 2001):
model was oversimplified no radiation pressure on dust,no size distributionpure N-body
unlikely if single passage P~1e-6
binary => ok, but repeated encounters delete structure
rings an artifact of a sharp edgein initial distribution of particles
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No ring features in more accurate simulations(Jeneskog, B.Sc. Thesis 2003)
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Augereau and Papaloizou (2003)
Stellar flyby (of an elliptic-obit companion) explains some featuresof HD 141569A
Application to Beta Pictoris less certain...
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Resonant pileupof dust due to planets
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Some models of structure in dusty disks rely on too limited a physics: ideally one needs to follow: full spatial distribution, velocity distribution, and size distribution of a collisional system subject to various external forces like radiation and gas drag -- that’s very tough to do! Resultant planets depend on all this.
Beta = 0.01
(monodispersed)
Vega
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Warp from inclined planet (model of beta Pictoris), Wyatt; Augereau & Paploizou.
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The danger of overinterpretation of structure
Are the PLANETS responsible for EVERYTHING we see? Are they in EVERY system?
Or are they like the Ptolemy’s epicycles, added each time we need to explain a new observation?
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FEATURES in disks:
blobs, clumps ■streaks, feathers ■rings (axisymm) ■rings (off-centered) ■inner/outer edges ■disk gaps ■warps ■spirals, quasi-spirals ■tails, extensions ■
ORIGIN:
■ dust migration in gas
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Type 0 (gas drag + radiation pressure)
Gas drag: Keplerian circular orbital velocity of solids, slightly subkeplerian rotation of gas in disk (pressure gradients)
headwind, orbital decay (inward)
(Adachi 1976, Weidenschilling 1977, ...)
Gas drag + radiation pressure: strongly subkeplerian orbital speed of solids affected by stellar radiation pressure
back-wind, fast outward migration
(Takeuchi&Artymowicz 2001, Lin & Klahr 2002, Thebault, Lecavelier, …)
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Migration:
Type 0 Dusty disks: structure from
gas-dust coupling (Takeuchi & Artymowicz 2001)
theory will help determine gas distribution
Gas disk tapersoff here
Predicted dust distribution: axisymmetric ring
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Dust avalanches and implications:
-- upper limit on dustiness-- the division of disks into gas-rich, transitional and gas-poor
-- non-axisymmetry !
Other reasons: ISM sandblasting radiative instabilities
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Radiative blow-out of grains (-meteoroids, gamma meteoroids)
Dust avalanches
Radiation pressure on dust grains in disks
Neutral (grey)scattering from s> grains
Repels ISM dust Disks = Nature, not nurture!
Enhanced erosion;shortened dust lifetime
Orbits of stable -meteoroids are elliptical
Dust migrates,forms axisymmetric rings, gaps
(in disks with gas)
Short disk lifetime
Size spectrum of dust has lower cutoff
Weak/no PAH emission
Quasi-spiral structure
Instabilities (in disks)1
Age paradox
Coloreffects
Limit on fIRin gas-free disks
DUST AVALANCHES
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FEATURES in disks:
blobs, clumps ■streaks, feathers ■rings (axisymm) ■rings (off-centered) ■inner/outer edges ■disk gaps ■warps ■spirals, quasi-spirals ■tails, extensions ■
ORIGIN:
■ dust blowout avalanches,■ episodic/local dust release
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Dust Avalanche (Artymowicz 1997)
= disk particle, alpha meteoroid ( < 0.5)
= sub-blowout debris, beta meteoroid ( > 0.5)
Process powered by the energy of stellar radiation N ~ exp (optical thickness of the disk * <#debris/collision>)
N
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The above example is relevant to HD141569A, a prototype transitional disk with interesting quasi-spiral structure. Conclusion:
60
2
1
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10~)20exp(~)exp(/
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IR
IR
Transitional disks MUST CONTAIN GAS or face self-destruction.Beta Pic is among the most dusty, gas-poor disks, possible.
the midplane optical thickness
Ratio of the infrared luminosity (IR excess radiation from dust) to the stellar luminosity; it gives the percentage of stellar flux absorbed, then re-emitted thermally
multiplication factor of debris in 1 collision (number of sub-blowout debris)
Simplified avalanche equation
Solution of the simplified avalanche growth equation
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60
2
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242
~)exp(~)exp(/
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rdrzrdrs
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IR
IR
#) derivation:
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Bimodal histogram of fractionalIR luminosity fIR
similar to that predicted by diskavalanche process
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source: Inseok Song (2004)
Bimodal histogram of fractionalIR luminosity fIR
similar to that predicted by diskavalanche process
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ISO/ISOPHOT data on dustiness vs. time Dominik, Decin, Waters, Waelkens (2003)
uncorrected ages corrected ages
ISOPHOT ages, dot size ~ quality of age ISOPHOT + IRAS
fd of beta Pic
-1.8
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transitional systems 5-10 Myr age
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Grigorieva, Artymowicz and Thebault (A&A, 2006)Comprehensive model of dusty debris disk (3D) with full treatmentof collisions and particle dynamics. ■ especially suitable to denser transitional disks supporting dust avalanches■ detailed treatment of grain-grain colisions, depending on material ■ detailed treatment of radiation pressure and optics, depending on material ■ localized dust injection (e.g., planetesimal collision)■ dust grains of similar properties and orbits grouped in “superparticles”■ physics: radiation pressure, gas drag, collisionsResults:■ beta Pictoris avalanches multiply debris by up to 200!■ spiral OR blob-like shape of the avalanche■ 50-500 km bodies must collide for observability in the innerb Pic disk, which isn’t very probable■ strong dependence on material properties and certain other model assumptions, but mostly on disk dustiness: 3 times larger than b Pic => planetesimal collisions likely!
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fIR =fd disk dustiness
OK!
Age paradox!
Gas-free modelingleads to a paradox==> gas required or episodic dust production
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Model of (simplified) collisional avalanche with substantialgas drag, corresponding to 10 Earth masses of gas in disk
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Main results of modeling of collisional avalanches:
1. Strongly nonaxisymmetric, growing patterns
2. Substantial almost exponential multiplication
3. Morphology depends on the amount and distribution of gas, in particular on the presence of an outer initial disk edge
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Beta = 4H/r = 0.1Mgas = 50 ME
Best model, Ardila et al (2005)
HD 141569A
5 MJ, e=0.6, a=100 AUplanet
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Spontaneous axisymmetry breaking in opticallythick disks
results in structure resembling gravitational instability
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In gas+dust disks which are optically thick in the radial direction there may be an interesting set of instabilities. Radiation pressureon a coupled gas+dust system that has a spiral density wave with wave numbers (k,m/r), is analogous in phase and sign to the forceor self-gravity. The instability is linear, pseudo-gravitational, and can be obtained from a WKB local analysis.
Forces of selfgravity Forces of radiation pressure in the
inertial frame
Forces of rad. pressure relativeto those on the center of the arm
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In gas+dust disks which are optically thick in the radial direction there may be an interesting set of instabilities. Radiation pressureon a coupled gas+dust system that has a spiral density wave with wave numbers (k,m/r), is analogous in phase and sign to the forceor self-gravity..
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r(this profile results from dust migration)
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FEATURES in disks:(9 types)
blobs, clumps ■ (5)streaks, feathers ■ (4)rings (axisymm) ■ (2)rings (off-centered) ■ (7)inner/outer edges ■ (5)disk gaps ■ (4)warps ■ (7)spirals, quasi-spirals ■ (8)tails, extensions ■ (6)
ORIGIN: (10 reasons)
■ instrumental artifacts, variable PSF, noise, deconvolution etc.■ background/foreground obj.■ planets (gravity)■ stellar companions, flybys■ dust migration in gas■ dust blowout, avalanches■ episodic release of dust■ ISM (interstellar wind)■ stellar wind, magnetism■ collective eff. (self-gravity)
Many (~50) possible connections !
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Not only planets but also
Gas + dust + radiation =>non-axisymmetric featuresincluding regular m=1
spirals, conical sectors, and multi-armed wavelets, as well
as blobs
Conclusion: